The present invention relates to data transmission methods, data transmission apparatuses, data receiving apparatuses, and a packet data structure and, more particularly, to a process of performing data transmission in packet units between a distribution server and a terminal while successively reproducing the data of received packets at the terminal.
For transmission of video (audio and video) data on the Internet, a download type transmission method and a stream type transmission method are currently employed.
In the download type transmission method, a video file transmitted from a distribution server is once copied at the terminal and, thereafter, data of the video file (video data) is reproduced. So, the terminal cannot perform data reproduction until the file transmission is completed. Therefore, the download type transmission method is not suitable for long-hours reproduction of video data or the like.
On the other hand, in the stream type transmission method, while video data or the like is transmitted from a distribution server to a terminal, received data is reproduced at the terminal.
Recently, a stream type transmission method using a protocol called RTP (Real-time Transport Protocol) which is defined in IETE RFC 1889, has mainly been used.
FIG. 28(a) is a diagram for explaining a video data transmission method according to the RTP.
With reference to FIG. 28(a), a distribution server (transmitting end) and a terminal (receiving end) such as a personal computer are connected by a cable in the Internet, such as modem, ISDN, or LAN, and transmission of video data is carried out between the server and the terminal by using the RTP.
In the data transmission according to the RTP, processes for the respective packets are synchronized between the transmitting end and the receiving end by using time stamps as time information, and asynchronous (late arrival) packets and packets affected by transmission errors are discarded at the receiving end. Further, discarded or lost packets are detected at the receiving end, according to the absence of sequence numbers given to these packets.
On the other hand, Internet applications utilizing mobile phones, for example, mail access and text information service, are advancing now, and infrastructure for high-speed radio data communication (high-speed packet communication of xe2x88x92384 kbps) is under preparation for practical use of the third generation mobile communication (W-CDMA: Wide band-Code Division Multiple Access).
FIG. 28(b) is a diagram illustrating a communication network for the above-described W-CDMA visual terminal.
Such communication network includes a radio transmission section. For example, when performing data transmission between a video distribution server and a visual terminal through a relay server, the section between the distribution server and the relay server is a cable transmission section by the Internet, but the section between the relay server and the visual terminal is a radio transmission section by a mobile phone network such as the W-CDMA.
However, the bit error rate in the radio transmission section is 10xe2x88x923 while the bit error rate in the cable transmission section is 10xe2x88x925 xcx9c10xe2x88x927, and the radio transmission quality becomes a problem in the RTP type data transmission method in which the reproduction quality depends on the end-to-end (server-to-terminal) transmission quality.
The present invention is made to solve the above-described problems and has for its object to provide a data transmission method, a data transmission apparatus, and a data receiving apparatus, which can improve the transmission quality in a radio section in real-time transmission.
Other objects and advantages of the invention will become apparent from the detailed description that follows. The detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the scope of the invention will be apparent to those of skill in the art from the detailed description.
According to a first aspect of the present invention, there is provided a data transmission method for performing continuous data transmission from the transmitting end to the receiving end in units of packets, each packet having additional information relating to its sequence number, priority, and data reproduction time at the receiving end, while successively reproducing data of packets received at the receiving end. This method comprising the steps of: at the transmitting end, giving priority information to each packet to be transmitted; and storing, as retransmission data, only data of packets the priorities of which are equal to or higher than a predetermined value, in a retransmission buffer; at the receiving end, when a transmission error is detected, detecting the priority information of an error packet; and when the detected priority is equal to or higher than the predetermined value, outputting a retransmission request for the error packet to the transmitting end by indicating the sequence number of this error packet; at the transmitting end, only when the data of the packet having the sequence number which is indicated by the retransmission request from the receiving end is stored in the retransmission buffer, retransmitting the data of this packet to the receiving end; and discarding the data stored in the retransmission buffer in order starting from a packet which cannot be in time for data reproduction at the receiving end. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a second aspect of the present invention, in the data transmission method of the first aspect, when the retransmission buffer is filled up to its capacity, an updating process is performed, in which the retransmission data are retained while the data stored in the retransmission buffer are discarded in order, starting from a packet of the earliest reproduction time, on the basis of the reproduction time of each packet stored in the retransmission buffer. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a third aspect of the present invention, in the data transmission method of the first aspect, when the data transmitted from the transmitting end to the receiving end is video data based on MPEG, a packet which contains data corresponding to frames coded by utilizing intra-frame correlation is regarded as a packet having a high priority. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a fourth aspect of the present invention, in the data transmission method of the first aspect, at the transmitting end, the additional information relating to the sequence number and the priority of a predetermined packet is also embedded in a subsequent packet to be transmitted after the predetermined packet; and at the receiving end, in the case where a transmission error has occurred in the predetermined packet and the additional information of the predetermined packet has an error, a retransmission request for the predetermined packet as an error packet is made on the basis of the additional information of the predetermined packet which is embedded in the subsequent packet, when the subsequent packet transmitted after the predetermined packet is received. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a fifth aspect of the present invention, in the data transmission method of the fourth aspect, at the transmitting end, the process of embedding the sequence number of a predetermined high priority packet in a subsequent packet which follows the predetermined high priority packet is continuously performed until a high priority packet next to the predetermined high priority packet is transmitted; and at the receiving end, the sequence number of another packet which is embedded in the received packet is extracted, and when a transmission error has occurred in the packet of the extracted sequence number, a retransmission request for this error packet is made by indicating the sequence number of this packet. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced .
According to a sixth aspect of the present invention, there is provided a data transmission apparatus for relaying data which are successively transmitted from the transmitting end in units of packets, each packet having additional information relating to its sequence number, priority, data reproduction time at the receiving end. This apparatus comprises: a receiving unit for receiving the packets transmitted from the transmitting end; a priority decision unit for deciding the priority of each of the received packets; a retransmission packet storage unit for storing packets the priorities of which are equal to or higher than a predetermined value, as retransmission packets, on the basis of the priority of each packet decided by the priority decision unit; a retransmission instruction receiving unit for receiving a retransmission request from a terminal at the receiving end; a retransmission decision unit for deciding whether retransmission of the packet for which the retransmission request has been made should be performed or not, on the basis of the retransmission request and the storage status of the retransmission packets in the retransmission packet storage unit; a transmission queue management unit for setting the transmission order of the received packets and the packets which have been decided as packets to be retransmitted, on the basis of the additional information; and a transmission unit for transmitting the data of these packets in the transmission order set by the management unit. Therefore, only the error packets the priorities of which are equal to or higher than a predetermined value can be retransmitted, whereby the transmission quality of a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a seventh aspect of the present invention, there is provided a data receiving apparatus for receiving data which are transmitted from the transmitting end in units of packets, each packet having additional information relating to its sequence number, priority, and data reproduction time at the receiving end, and successively reproducing the data for each packet. This apparatus comprises: a receiving unit for receiving the packets transmitted from the transmitting end; an error packet detection unit for detecting error packets in which errors have occurred during transmission, and outputting normal packets which have been transmitted without transmission errors, on the basis of the data of the received packets; a packet priority decision unit for receiving the output from the error packet detection unit, and deciding error packets the priorities of which are equal to or higher than a predetermined value; and a retransmission instruction output unit for outputting a retransmission request for each of the error packets the priorities of which are decided as being equal to or higher than the predetermined value, to the transmitting end, by indicating the sequence number of this error packet. Therefore, at the receiving end, a retransmission request to the transmitting end is made only for the error packet the priority of which is equal to or higher than a predetermined value, whereby the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to an eighth aspect of the present invention, there is provided a data transmission method in which data transmission from the transmitting end to the receiving end is continuously performed in units of packets, each packet having additional information relating to its sequence number, priority, and data reproduction time at the receiving end, while successively reproducing data of packets which have arrived at the receiving end and, at this time, only packets which can be in time for data reproduction at the receiving end are retransmitted. This method comprises: at the transmitting end, giving a data reproduction time at the receiving end to each packet to be transmitted; and storing, as retransmission data, only data of packets the priorities of which are equal to or higher than a predetermined value, in a retransmission buffer; at the receiving end, when a transmission error is detected, detecting the reproduction time for an error packet and the arrival time of the error packet, and deciding an arrival time limit in accordance with the reproduction time; and when the error packet has arrived before the arrival time limit, outputting a retransmission request for the error packet to the transmitting end by indicating the sequence number of this error packet; at the transmitting end, when the data of the packet having the sequence number indicated by the retransmission request from the receiving end is stored in the retransmission buffer, retransmitting data of the packet the transmission time of which does not pass the reproduction time, to the receiving end, while discarding data of the packet the transmission time of which has passed the reproduction time; and discarding the data stored in the retransmission buffer in order starting from a packet which cannot be in time for data reproduction at the receiving end. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a ninth aspect of the present invention, in the data transmission method of the eighth aspect, when the retransmission buffer is filled up to its capacity, an updating processes is performed, in which the retransmission data are retained while the data stored in the retransmission buffer are discarded in order, starting from a packet of the earliest reproduction time, on the basis of the reproduction time of each packet stored in the retransmission buffer. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a tenth aspect of the present invention, in the data transmission method of the eighth aspect, the arrival time limit is decided based on at least one of the allowable packet delay time decided at the receiving end, and the packet transmission delay time between the transmitting end and the receiving end. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to an eleventh aspect of the present invention, in Ache data transmission method of the eighth aspect, at the Transmitting end, additional information relating to the sequence number and the reproduction time corresponding to a target packet to be transmitted is embedded in a subsequent packet to be transmitted after the target packet; and at the receiving end, when a transmission error of the target packet has occurred and the additional information of the target packet has an error, a retransmission request for the target packet as an error packet is made on the basis of the additional information of the target packet which is embedded in the subsequent packet, when the subsequent packet transmitted after the target packet is received. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a twelfth aspect of the present invention, there is provided a data transmission apparatus for relaying data which are successively transmitted from the transmitting end in units of packets, each packet having additional information relating to its sequence number, priority, data reproduction time at the receiving end. This apparatus comprises: a receiving unit for receiving the packets transmitted from the transmitting end; a priority decision unit for deciding the priority of each of the received packets; a reproduction time decision unit for deciding packets which cannot be in time for reproduction at the receiving end, amongst the packets to be transmitted to the receiving end; a retransmission packet storage unit for storing packets the priorities of which are equal to or higher than a predetermined value, as retransmission packets, on the basis of the priority of each packet decided by the priority decision unit; a retransmission instruction receiving unit for receiving a retransmission request from a terminal at the receiving end; a retransmission decision unit for deciding whether retransmission of the packet for which the retransmission request has been made should be performed or not, on the basis of the retransmission request and the storage status of the retransmission packets in the retransmission packet storage unit; a transmission queue management unit for setting the transmission order of the received packets and the packets which have been decided as packets to be retransmitted, on the basis of the additional information; and a transmission unit for transmitting, in the transmission order set by the management unit, the data of packets other than the packets which are decided as packets that cannot be in time for reproduction at the receiving end, by the reproduction time decision unit. Therefore, the transmission. quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a thirteenth aspect of the present invention, there is provided a data receiving apparatus for receiving data which are transmitted from the transmitting end in units of pickets, each packet having additional information relating to its sequence number, priority, and data reproduction time at the receiving end, and successively reproducing the data for each packet. This apparatus comprises: a receiving unit for receiving the packets transmitted from the transmitting end; an error packet detection unit for detecting error packets in which errors have occurred during transmission, and outputting normal packets which have been transmitted without transmission errors, on the basis of the data of the received packets; a reproduction time decision unit for detecting the reproduction time given to each error packet detected by the error packet detection unit and the arrival time of the error packet at the receiving end, and setting the arrival time limit based on the reproduction time, and deciding whether or not the error packet has arrived at the receiving end before the arrival time limit; and a retransmission instruction output unit for outputting a retransmission request only for the error packet which has arrived at the receiving end before the, arrival time limit, to the transmitting end, by indicating the sequence number of the error packet, on the basis of the result of the decision in the reproduction time decision unit. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a fourteenth aspect of the present invention, there is provided a data transmission method for performing continuous data transmission from the transmitting end to the receiving end in units of packets, each packet having additional information relating to its sequence number, priority, and data reproduction time at the receiving end, while successively reproducing data of packets arrived at the receiving end. This method comprises: at the transmitting end, giving a data reproduction time and priority information to each packet to be transmitted; and storing, as retransmission data, only data of packets the priorities of which are equal to or higher than a predetermined value, in a retransmission buffer; at the receiving end, when a transmission error is detected, detecting the priority information of an error packet, the reproduction time of the error packet, and the arrival time of the error packet; setting the arrival time limit of the error packet on the basis of the reproduction time; and when the detected priority is equal to or higher than the predetermined value and the error packet has arrived before the arrival time limit, outputting a retransmission request for this error packet to the transmitting end by indicating the sequence number of this error packet; at the transmitting end, when data of the packet having the sequence number indicated by the retransmission request from the receiving end is stored in the retransmission buffer, retransmitting only data of the packet the transmission time of which does not pass the reproduction time, to the receiving end, while discarding data of the packet the transmission time of which has passed the reproduction time; and discarding the data stored in the retransmission buffer in order starting from a packet which cannot be in time for reproduction at the receiving end. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a fifteenth aspect of the present invention, in the data transmission method of the fourteenth aspect, at the transmitting end, additional information relating to the sequence number, the priority, and the reproduction time of a predetermined packet is embedded in a subsequent packet to be transmitted after the predetermined packet; and at the receiving end, when a transmission error of the predetermined packet has occurred and the additional information of the predetermined packet has an error, a retransmission request for the predetermined packet as an error packet is made on the basis of the additional information of the predetermined packet which is embedded in the subsequent packet, when the subsequent packet transmitted after the predetermined packet is received. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a sixteenth aspect of the present invention, in the data transmission method of the fifteenth aspect, at the transmitting end, the process of embedding the sequence number of a predetermined high priority packet in a subsequent packet which follows the predetermined high priority packet is continuously performed until a high priority packet next to the predetermined high priority packet is transmitted; and at the receiving end, the sequence number of another packet which is embedded in the received packet is extracted, and when a transmission error has occurred in the packet of the extracted sequence number, a retransmission request for this packet is made by indicating the sequence number of this packet. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a seventeenth aspect of the present invention, in the data transmission method of the fifteenth aspect, at the transmitting end, when additional information relating to the sequence number and the reproduction time corresponding to each packet is embedded in a subsequent packet to be transmitted after the packet, a difference between additional information relating to the sequence number and the reproduction time corresponding to the subsequent packet and the additional information relating to the sequence number and the reproduction time corresponding to the previous packet is embedded as the additional information. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to an eighteenth aspect of the present invention, there is provided a data transmission method for performing data transmission between a distribution server and a terminal through a relay server in units of packets, and successively reproducing data of packets received at the terminal. This method comprising: when a transmission error has occurred between the relay server and the terminal, performing retransmission of an error packet by the relay server in response to a retransmission request from the terminal; and when a transmission error has occurred between the distribution server and the relay server, performing retransmission of an error packet by the distribution server in response to a retransmission request which has been transmitted from the terminal through the relay server. Therefore, the number of retransmission times is reduced between the distribution server and the relay server.
According to a nineteenth aspect of the present invention, in the data transmission method of the eighteenth aspect, when a transmission error has occurred between the distribution server and the relay server, a retransmission request is transmitted from the relay server to the distribution server, and retransmission of an error packet to the relay server is performed by the distribution server. Therefore, wasteful transmission of error packets from the relay server to the terminal is avoided.
According to a twentieth aspect of the present invention, there is provided a data transmission apparatus for relaying data which are successively transmitted from a distribution server, in units of packets each having additional information relating to its sequence number, priority, data reproduction time at the receiving end. This apparatus comprises: a receiving unit for receiving the packets transmitted from the transmitting end; a priority decision unit for deciding the priority of each of the received packets; a retransmission packet storage unit for storing packets the priorities of which are equal to or higher than a predetermined value, as retransmission packets, on the basis of the priority of each packet decided by the priority decision unit; a retransmission instruction receiving unit for receiving a retransmission request from a terminal at the receiving end; a retransmission decision unit for deciding whether retransmission of the packet for which the retransmission request has been made is to be performed or not, on the basis of the retransmission request and the storage status of the retransmission packets in the retransmission packet storage unit; a retransmission instruction output unit for outputting the retransmission request for the error packet requested by the terminal, to the distribution server, on the basis of the result of the decision in the retransmission decision unit; a transmission queue management unit for setting the transmission order of the received packets and the packets which have been decided as packets to be retransmitted, on the basis of the additional information; and a transmission unit for transmitting the data of these packets in the transmission order set by the management unit. Therefore, the number of retransmission times between the distribution server and the relay server can be reduced.
According to a twenty-first aspect of the present invention, there is provided a data transmission method for performing continuous data transmission from the transmitting end to the receiving end in units of packets, each packet having additional information relating to its sequence number, priority, and data reproduction time at the receiving end, while successively reproducing data of packets received at the receiving end. This method comprises: at the transmitting end, when a packet the priority of which is equal to or higher than a predetermined value is transmitted as a high priority packet, storing data of this high priority packet, as retransmission data, in a retransmission buffer; managing the value of the transmitting end high priority sequence number which corresponds to the number of transmitted high priority packets, and the value of the sequence number of the high priority packet so that these values are correlated with each other; and transmitting a subsequent packet which follows the high priority packet after embedding the value of the transmitting end high priority sequence number in this subsequent packet; at the receiving end, extracting the value of the transmitting end high priority sequence number which is embedded in the received packet; managing the value of the receiving end high priority sequence number which corresponds to the number of received high priority packets; when the value of the extracted transmitting end high priority sequence number is not equal to the value of the receiving end high priority sequence number, outputting a retransmission request to the transmitting end, by indicating the value of the transmitting end high priority sequence number which is obtained on the basis of the value of the receiving end high priority sequence number; and updating the value of the receiving end high priority sequence number; at the transmitting end, only when data of the packet having the sequence number corresponding to the value of the transmitting end high priority sequence number which is indicated by the retransmission request from the receiving end is stored in the retransmission buffer, retransmitting the data of this packet to the receiving end. Therefore, retransmission of the high priority packet the priority of which is equal to or higher than a predetermined value, can be performed by simpler procedures.
According to a twenty-second aspect of the present invention, in the data transmission method of the twenty-first aspect, at the receiving end, when the value of the transmitting end high priority sequence number embedded in the received packet is not equal to the value of the receiving end high priority sequence number, a retransmission request is output to the transmitting end, by listing the values ranging from the value obtained by adding 1 to the receiving end high priority sequence number, to the value of the transmitting end high priority sequence number, as the values of the transmitting end high priority sequence numbers, or by designating the range as the range of the values of the transmitting end high priority sequence numbers; and at the transmitting end, the sequence numbers corresponding to the values of the plural transmitting end high priority sequence numbers which are indicated by the retransmission request from the receiving end are retrieved, and only when data of the packets having the sequence numbers obtained by the retrieval are stored in the retransmission buffer, the data of the packets are retransmitted to the receiving end. Therefore, retransmission of the high priority packet the priority of which is equal to or higher than a predetermined value, can be performed by simpler procedures.
According to a twenty-third aspect of the present invention, in the data transmission method of the twenty-first aspect, at the receiving end, the retransmission request is performed continuously several times, indicating the value of a transmitting end high priority sequence number; and at the transmitting end, the sequence number corresponding to the value of the transmitting end high priority sequence number which is indicated by the retransmission request from the receiving end is retrieved, and data of the packet having the sequence number obtained by the retrieval is retransmitted to the receiving end and, simultaneously, the correspondence between the value of the sequence number obtained by the retrieval and the value of the transmitting end high priority sequence number indicated by the receiving end is deleted. Therefore, when at least one of several transmission requests from the receiving end is normally received at the transmitting end, only the error packet the priority of which is equal to or higher than a predetermined value can be retransmitted, whereby the transmission quality in a radio section in real-time transmission can be effectively improved.
According to a twenty-fourth aspect of the present invention, there is provided a data transmission apparatus for relaying data which are successively transmitted from the transmitting end in units of packets, each packet having additional information relating to its sequence number, priority, data reproduction time at the receiving end. This apparatus comprises: a receiving unit for receiving the packets transmitted from the transmitting end; a transmission queue management unit for setting the transmission order of the received packets and packets which are decided as packets to be retransmitted; a transmission unit for transmitting data of these packets in the transmission order set by the transmission queue management unit; a priority decision unit for deciding the priority of each of the received packets; a retransmission packet storage unit for storing packets the priorities of which are equal to or higher than a predetermined value, as retransmission packets, on the basis of the priority of each packet decided by the priority decision unit; a sequence number management unit for managing the value of the transmitting end high priority sequence number which corresponds to the number of transmitted high priority packets, and the value of the sequence number of the high priority packet so that these values are correlated with each other; a high priority sequence number insertion unit for embedding the value of the transmitting end high priority sequence number in a subsequent packet which follows the high priority packet; a retransmission instruction receiving unit for receiving a retransmission request indicating the high priority sequence number, from a terminal at the transmitting end; and a retransmission decision unit for deciding whether retransmission of the packet for which the retransmission request has been made is to be performed or not, on the basis of the retransmission request and the storage status of the retransmission packets in the retransmission packet storage unit. Therefore, only the error packet the priority of which is equal to or higher than a predetermined value can be retransmitted, whereby retransmission of the high priority packet can be performed by simpler procedures.
According to a twenty-fifth aspect of the present invention, there is provided a data receiving apparatus for receiving data which are transmitted from the transmitting end in units of packets, each packet having additional information relating to its sequence number, priority, and data reproduction time at the receiving end, and successively reproducing the data for each packet. This apparatus comprises: a receiving unit for receiving the packets transmitted from the transmitting end; an error packet detection unit for detecting an error packet in which an error has occurred during transmission, and outputting a normal packet which has been transmitted without transmission errors, and the value of the transmitting end high priority sequence number which corresponds to the number of transmitted high priority packets and is embedded in the normal packet; a high priority sequence number management unit for managing the value of the receiving end high priority sequence number which corresponds to the number of normal high priority packets which have been received without transmission errors, on the basis of the output from the error packet detection unit; a retransmission sequence number decision unit for comparing the value of the transmitting end high priority sequence number from the error packet detection unit with the value of the receiving end high priority sequence number, and when these values are not equal, deciding the value of the transmitting end high priority sequence number for which a retransmission request is to be made, on the basis of the value of the receiving end high priority sequence number; and a retransmission instruction output unit for outputting a retransmission request to the transmitting end, by indicating the value of the decided transmitting end high priority sequence number. Therefore, retransmission of the high priority packet can be performed with simpler procedures.
According to a twenty-sixth aspect of the present invention, there is provided a data structure of a packet for performing data transmission from the transmitting end and the receiving end, wherein the packet comprises a header section containing relevant information indicating the attribute of the packet, and a data section containing data to be transmitted; and the header section comprises at least first and second header information, amongst first header information indicating the sequence number corresponding to the packet, second header information indicating the priority of the packet, and third header information indicating the reproduction time at the receiving end, of the data to be transmitted. Therefore, retransmission of a low priority packet and retransmission of a packet which cannot be in time for reproduction can be avoided, whereby the transmission quality in a radio section in real-time transmission is improved while reducing the number of retransmission times.
According to a twenty-seventh aspect of the present invention, in the packet data structure of the twenty-sixth aspect, the header section of the packet includes attribute information of a packet which has already been transmitted before the packet. Therefore, retransmission of an error packet can be performed with reliability.
According to a twenty-eighth aspect of the present invention, in the packet data structure of the twenty-seventh aspect, the header section of the packet includes the first and second information or the first and third information, as attribute information of a packet which has already been transmitted before the packet. Therefore, retransmission control based on the priority or the reproduction time can be performed with reliability.
According to a twenty-ninth aspect of the present invention, in the packet data structure of the twenty-sixth aspect, the header section of the packet includes the value of the high priority sequence number corresponding to the number of high priority packets which have been transmitted before the packet and having the priorities equal to or higher than a predetermined value. Therefore, the transmission quality in a radio section in real-time transmission is improved and, moreover, retransmission of an error packet is realized by simpler procedures.